Apple this morning announced that OS X Mountain Lion has been downloaded three million times in the four days following its release last Thursday, making it the most successful OS X release in the company’s history.

Its predecessor, OS X Lion, clocked in Lion a million downloads on its first day on the Mac App Store, moving six million copies in total during its first 76 days.

Mountain Lion is being distributed exclusively via the Mac App Store and is priced at $19.99 a copy, with rights to install it on up to five different Macs. In other words, Apple made a cool $60 million in revenue off Mountain Lion in just four days…

The three million downloads translate into more than six percent of Apple’s OS X user base pegged at 66 million people as of last month, 40 percent of which are running OS X Lion. Apple also said at WWDC it has sold 26 million copies of Mac OS X Lion since its launch last summer.

“Just a year after the incredibly successful introduction of Lion, customers have downloaded Mountain Lion over three million times in just four days, making it our most successful release ever,” said Philip Schiller, Apple’s senior vice president of Worldwide Marketing.

Mountain Lion comes with 200 new features, including PowerNap to keep data on your notebook up to date while in sleep mode, AirPlay Mirroring of your Mac’s display to your television through the Apple TV set-top box, Notification Center, iMessage, Game Center, all-new Notes and Reminders apps and of course Twitter and Facebook (coming this fall) integration via the standard sharing button known from iOS.

Also new: Siri voice dictation, enhanced Safari with shared tabs via iCloud, better Mail with VIP recipients, tighter iCloud integration system-wide featuring support for Documents in the Cloud, iCloud documents storage access in standard Open/Save dialog boxes, Gatekeeper which only allows for downloads and installs of signed and sandboxed applications from the Mac App Store and more.